1. Field of the Invention
The present invention concerns a device for handling and guiding bundles with vertical sheet stackers.
2. Description of Related Art
With known vertical sheet stackers, the sheets arrive at the stacker from the rotary press in the form of a continuous overlapping stream, like scales, and are then gathered up by the stacker to form a bundle of a determined height, the sheets being superposed one on top of the other. It is a common feature of a known type of stacker that for the initial stage of bundle formation a so-called vane separator is used, retractable and capable of oscillating, which is designed to be positioned in the incoming stream of sheets; this vane then transfers the sheets starting to be formed into a bundle onto a fork support that can be shifted downwards, and the formation of the bundle is completed on this fork. As soon as the bundle is completed, the fork is rapidly lowered onto an L-shaped roller conveyor underneath, linking the bundling station with the associated binding station, from where the secured bundles are then conveyed to a palletizer.
It is well-known that with vertical stackers the rapid lowering of the finished bundle onto the roller conveyor underneath is a very delicate handling operation, as the sheets are loosely arranged on top of one another, and the degree of compactness in the bundle becomes increasingly less from the bottom of the pile upwards, since its compactness is determined solely by the weight of the superposed sheets. As a result, during this rapid descent stage the bundle expands, with the well-known concertina effect, especially in the top part. This expansion makes the bundle arch out towards the outside of the stacker. The extent of this expansion, or bending outwards, varies in accordance with a variety of factors, including the type of paper used for the sheets, the number of folds provided for in the sheets, and so on. Such expansion is, for example, fairly significant in the case of sheets that are folded into three, since they will then have one side that is thicker than the rest of the sheet. Moreover, a certain amount of air will remain trapped between individual pages with these sheets. These conditions therefore heighten the "suction" effect to which the bundle is subjected at the top in its rapid descent, which provokes undulation between individual sheets so that they are liable to slide about on top of one another. As a consequence, the arrangement of the sheets in the top part of the bundle begins to break up, leading to the arching outwards that has been mentioned. Disarrangements of this kind create various problems when it comes to subsequent handling of the bundles. In the first place there are problems regarding conveyance of the finished bundles from the stacking station to the adjoining binding station, since further disarrangements may occur in the course of such conveyance, and the sheets at the top may come away from the bundle altogether. There are other problems at the binding stage. The sheets, or wads of sheets, at the top of the bundle are out of true with one another, that is to say, they project beyond the ideal contour of the bundle, and the sheets that project in this way become damaged by the securing straps and their subsequent handling while being palletized. The Italian Patent application No. 20344 A/83 , now Italian Patent No. 1,163,186, proposes equipping the vertical stacker with a trolley with oscillating sides in order to ensure that the sides of the bundle stay in the correct position during conveyance from the stacking to the binding station. Such trolleys, therefore, act only on the sides of the bundles, and are not capable of overcoming the difficulties referred to above.
Further, in U.S. Pat. No. 4,554,867 provision is made for mounting on the sides of a so-called trolley longitudinal cylinder/piston units on the free upper end of whose piston rods is attached a transverse cylinder/piston unit. After the bundle has been completed and lowered in a rapid descent onto the roller conveyor, and the sides of the trolley have been closed in a rotary movement against the bundle, the piston rods of the transverse cylinder/piston units are expelled so that they are positioned above the bundle. Next the piston rods of the longitudinal cyclinder/piston units are retracted, causing initial compression of the bundle before it is conveyed to the binding station. Clearly, this pressure on the bundle is effected after the disarrangements of the sheets referred to above will have taken place, so that neither is this action by the trolley capable of overcoming the difficulties already mentioned.